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| Involute Gears - Identification of Pressure Angle. |
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| Pete W.:
Hi there, all, :mmr: N.B.: this is NOT a 'for sale' posting! I am having a 'spring clean' in my workshop :clap: :clap: :clap: :clap: :clap: :clap: and have discovered a number of gearwheels that are surplus to requirements. I am about to compile a description prior to listing them on a well-known auction site and I like my listing descriptions to be complete and accurate. I know how to determine the D.P. (they are Imperial) of these gears and measurement of the thickness and centre hole dimensions is straightforward. I would like to include the pressure angle in my description. However, I have no idea how to measure that parameter. :scratch: :scratch: :scratch: :scratch: :scratch: :scratch: Wikipedia states that 20° is the usual value but that 14½° is a less common value. I have read that both values are found on various lathe gearwheels. So, my question is: is there a simple measurement procedure, using equipment I am likely to have, that would enable me to distinguish between 20° and 14½° pressure angle? (I do not possess a gear-tooth vernier gauge.) |
| DMIOM:
Pete - not sure if they're any use but have a look at this or this (courtesy Mr Google) Dave |
| Pete W.:
Hi there, Dave, Thank you for your reply. :bow: :thumbup: :bow: :thumbup: :bow: :thumbup: I had done a Google search but I missed those links. The first one looks like the way I should go - just a vernier caliper, a pencil, the back of an envelope and, if a senior moment blitzes my arithmetic, break glass and deploy the slide rule! :D :D :D |
| Lew_Merrick_PE:
--- Quote from: Pete W. on September 02, 2013, 08:41:04 AM ---Wikipedia states that 20° is the usual value but that 14½° is a less common value. --- End quote --- Which should warn you about Wikipedia -- 14-1/2° PA was the primary standard for inch-based gear well into the 1970's. 20° PA entered usage during WWI, but did not become common for gear until the early-/mid-1960's. One of my premiere screw-ups as an apprentice was failing to recognize the difference (because apprentice texts of that time assumed 14-1/2° PA as a matter of course). |
| Pete W.:
Hi there, Lew, Thank you for that warning. |
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